PESEL (PolishPowszechny Elektroniczny System Ewidencji Ludności, Universal Electronic System for Registration of the Population) is the national identification number used in Poland since 1979. It always has 11 digits, identifies just one person and cannot be changed to another one.

The PESEL number is mandatory for all permanent residents of Poland and for temporary residents living in Poland for over 2 months. Applicants for Polish citizenship must request a PESEL number together with their passport application.

The PESEL was the system designed by the communist government (during PRL) to trace a personal information about every citizen. Itself is the direct "child" of the previous system MAGISTER (called identically like msc. studies degree in Poland), which was designed to trace and record data about "most dangerous to system and communist power" people, which basically as a danger was treated everyone with university degree.[1]

It has the form of YYMMDDZZZXQ, where YYMMDD is the date of birth (with century encoded in month field), ZZZ is the personal identification number, X denotes sex (even number for females, odd number for males) and Q is a control digit, which is used to verify whether a given PESEL is correct or not.

Having a PESEL in the form of ABCDEF GHIJK, one can check the vailidity of the number by computing the following expression:

A*1 + B*3 + C*7 + D*9 + E*1 + F*3 + G*7 + H*9 + I*1 + J*3

Then the last digit of the result should be subtracted from 10. If the result of the last operation is not equal to the last digit of a given PESEL, the PESEL is incorrect. This system works reliably well for catching one-digit mistakes and digit swaps.

Checking validity of PESEL: 44051401358 (number 8, the last digit, is the check digit for this PESEL):

A similar system of statistical identification numbers exists for businesses, called REGON (from Rejestr Gospodarki Narodowej – Register of the National Economy). Also all business taxpayers (prior to September 2011 – all taxpayers) have a tax identification number called NIP(Numer Identyfikacji Podatkowej).

Individuals in Poland are often asked to provide the number of their national identity card(dowód osobisty) as identification (foreign citizens give their passport number instead). Similarly, businesses and corporations are often required to state the number at which they appear in the register of businesses or similar.